Insect pests are a major factor in the loss of the world's commercially important agricultural crops. Broad spectrum chemical pesticides have been used extensively to control or eradicate pests of agricultural importance. There is, however, substantial interest in developing effective alternative pesticides.
Microbial pesticides have played an important role as alternatives to chemical pest control. The most extensively used microbial product is based on the bacterium Bacillus thuringiensis (Bt). Bt is a gram-positive spore forming Bacillus which produces an insecticidal crystal protein (ICP) during sporulation.
Numerous varieties of Bt are known that produce more than 25 different but related ICP's. The majority of ICP's made by Bt are toxic to larvae of certain insects in the orders epidoptera, Diptera and Coleoptera. In general, when an ICP is ingested by a susceptible insect the crystal is solubilized and transformed into a toxic moiety by the insect gut proteases. None of the ICP's active against coleopteran larvae such as Colorado potato beetle (Leptinotarsa decemlineata) or Yellow mealworm (Tenebrio molitor) have demonstrated significant effects on members of the genus Diabrotica particularly Diabrotica virgifera virgifera, the western corn rootworm (WCRW) or Diabrotica longicornis barberi, the northern corn rootworm.
Bacillus cereus (Bc) is closely related to Bt. A major distinguishing characteristic is the absence of a parasporal crystal in Bc. Bc is a widely distributed bacterium that is commonly found in soil and has been isolated from a variety of foods and drugs. The organism has been implicated in the spoilage of food.
Although Bt has been very useful in controlling insect pests, there is a need to expand the number of potential biological control agents.